The present invention relates to sputtering apparatus and film-forming processes using them.
Organic EL devices have recently attracted attention as display devices.
FIG. 10 is a schematic cross-sectional diagram for illustrating the structure of an organic EL device 201.
This organic EL device 201 includes a lower electrode 214, organic layers 217, 218 and an upper electrode 219 deposited in this order on an object to be film-formed 211, whereby light is emitted in or at the interfaces of the organic layers 217, 218 when a voltage is applied across the upper electrode 219 and the lower electrode 214. If the upper electrode 219 is formed of a transparent conductive film (such as, an ITO film (indium tin oxide film)), the emitted light passes through the upper electrode 219 and emit to the outside.
The upper electrode 219, as described above, is mainly formed by vapor deposition.
Vapor deposition has the advantage of forming good interfaces without damaging organic films 217, 218 when protective films for the upper electrode 219 or organic EL device are formed because particles released by sublimation or evaporation from a vapor deposition source are neutral low-energy particles (about several electron volts).
However, it has the disadvantages that dark spots may be generated or electrodes may be separated by long-term operation because films formed by vapor deposition poorly adhere to organic films. In terms of productivity, it has disadvantages; such as, difficulty in thickness distribution for large area due to the point evaporation source, deterioration of evaporation boat and short maintenance cycles due to difficulty in continuous feeding.
A possible solution to the above-mentioned problems is sputtering. However, sputtering with parallel board-shaped targets, wherein the object is opposed to the surface of the target, has disadvantages in that luminescence starting voltage is very high or no luminescence occurs in activation tests of organic EL devices when an upper electrode made of aluminum is formed on an organic layer. This results from the fact that charged particles in a plasma (Ar ions, secondary electrons, recoil Ar ions) or sputtered particles having high kinetic energy enter onto the organic film and destroy the interface of the organic film to hinder favorable injection of electrons.
Thus, strategies were investigated in the conventional technologies, among which a sputtering apparatus 110 as shown in FIG. 11 was proposed. This sputtering apparatus 110 has a vacuum chamber 11, wherein two targets 121a, 121b are fixed to backing plates 122a, 122b at their back surfaces while their surfaces are opposite with each other in parallel at a predetermined distance therebetween in the vacuum chamber 111.
Magnet members 115a, 115b are provided toward the back surfaces of the backing plates 122a, 122b. The magnet members 115a, 115b comprise annular magnets 123a, 123b fixed to yokes 129a, 129b. 
Each of the magnets 123a, 123b has one magnetic pole facing the targets 121a, 121b and the other magnetic pole facing the opposed direction to the targets, and the magnetic poles of the two magnets 123a, 123b facing targets 121a, 121b have opposite polarities. Consequently, when the north pole of one magnet 123a faces the target 121a, the south pole of the other magnet 123b faces the target 121b, whereby magnetic field lines are generated between the two magnets 123a, 123b. The magnetic field lines generated between the magnets 123a, 123b are cylindrical because the magnets 123a, 123b are annular.
When the vacuum chamber 111 is evacuated by an evacuation system 116 and a sputtering gas is introduced from a gas feed system 117 and a voltage is applied to the targets 121a, 121b, a plasma of the sputtering gas is generated in the space between the targets 121a, 121b so that the surfaces of the targets 121a, 121b are sputtered.
An object to be film-formed 113 is placed laterally to the space between the targets 121a, 121b, and a thin film is formed on the surface of the object 113 by sputtered particles ejected in a slant direction from the targets 121a, 121b and released into the vacuum chamber 111.
In this sputtering apparatus 110, the plasma is not leaked toward the object 113 because the space between the opposed targets 121a, 121b is enclosed by cylindrical magnetic field lines formed between the two magnets 123a, 123b and the plasma is confined by the magnetic field lines. Thus, the object 113 is not exposed to charged particles in the plasma, and the organic thin film exposed on the surface of the object 113 is not damaged.
In the sputtering apparatus 110, however, a phenomenon occurs in which targets 121a, 121b are more deeply etched in center parts than peripheral parts by sputtering. Reference numbers 131a, 131b in FIG. 12 represent eroded regions where targets 121a, 121b are deeply etched and the thickness is reduced, and reference numbers 132a, 132b in the same figure represent uneroded regions where targets 121a, 121b are not etched and the thickness remains large.
The targets 121a, 121b must be changed before the targets 121a, 121b are etched so deeply to expose the backing plates 122a, 122b at their back surfaces because an abnormal discharge occurs.
In the conventional sputtering apparatus 110, the target utilization efficiency is low because the targets 121a, 121b had to be changed when the targets 121a, 121b are deeply etched only in parts even if the thickness is less reduced in the remaining parts. These problems are disclosed in JPA 11-162652 and JPA 2005-032618, for example.